NEW YORK CITY -- Americans have been losing their love for carbonated drinks for years, but sales of diet soda are falling the fastest, according to newly released Wells Fargo research.

Sales of zero- and low-calorie soda plunged 6.8% in the past year, while sales of regular sodas dropped 2.2%, according to Wells Fargo, citing Nielsen data. As a category, diet soda has contracted more than regular soda for three straight years.

Most likely fueling diet soda's downward trend is mounting public awareness and about the potential harmful health effects of artificial sweeteners cited in several studies. Aspartame, in particular, has been linked to cancer in some studies, dating back to the 1970s. The FDA, which approved the sweetener in 1981, says those studies were flawed.

The American Beverage Association defends artificial sweeteners as being among "the most studied and reviewed ingredients'' over four decades.

Coke launched an advertising campaign this summer, defending aspartame by highlighting 200-plus studies that support its safety.

Meanwhile, the beverage giants are working to reformulate their diet drinks with new sweeteners, including those derived from natural sources like the stevia plant.

PepsiCo removed aspartame from its mid-calorie Pepsi Next last spring and said it plans to launch a new diet soda next year. Coke began selling its stevia-sweetened, mid-calorie Coca-Cola Life in South America earlier this year and is reportedly developing a new stevia-based sweetener.